The Syrian Revolution General Commission said it tallied 825 non-combatants it said were killed by government forces in clashes across the country.
The commission told Turkey's Anadolu news service the toll was the highest in Damascus and Aleppo, where rebels and government troops have been battling in the streets for several months.
The Syrian regime said its forces were also active in the countryside. The official SANA news agency said so-called terrorist units were wiped out in several villages and at least five vehicles fitted with machine guns were destroyed.
The Syrian army has also been taking a toll on the nation's history, The New York Times said.
Archaeological sites around Syria have come under increasing pressure as the security situation deteriorates. Rebel volunteers have been doing their best to secure various sites to protect them from looters.
An official of the government antiquities ministry told the Times he had repeatedly asked the military to keep its ground troops clear of sensitive sites. Troops have used the locations as camps and have caused collateral damage by digging bunkers and running heavy vehicles close to fragile tunnels and structures.